Transformer core and method of making the same



NOV. 5, 1940. SANDERS 2,220,732

TRANSFORMER CORE AND METHOD OF MAKING THE SAME Filed Jan. 25, 1938 4 Sheets-Sheet l Inventor NOV. 5, 3940. M. SANDERS 2.220132 TRANSFORMER CORE AND METHOD OF MAKING THE SAME Filed Jan. 25, 1938 4 Sheets-Sheet 2 in venfor {Xe/w Afiorneys TRANSFORMER CORE AND METHOD OF MAKING THE SAME 4 Sheets-Sheet 3 Nov. 5, 1940. H. M. SANDERS Filed Jan. 25, 1938 By fi Aiiorneus 1940- H. M. SANDERS 2,220,732

TRANSFORMER CORE AND METHOD OF MAKING THE SAME 4 Sheets-Sheet 4 Filed Jan. 25, 1938 A tiorneys Patented Nov. 5,1940 7 PATENT oFncE TRANSFORMER 001m AND METHOD OF MAKING THE SAME Homer M. Sanders, Sharon, Pa., assignor to General Electric Company, a corporation of New York Application January 25,1938, Serial No. 186,895

3 Claims.

My invention relates in general to'inductive electrical apparatus having continuous magnetic circuits, and particularly to electrical transformers, and the method of producingthe same,

6 and important objects of the invention are, to improve the electrical and magnetic circuits of continuous core inductive electrical apparatus; to facilitate the assembly of the laminations constituting the magnetic circuits; and the application of the coils and insulation constituting the electrical circuits in proper relation to the assembled cores. i

It is a further important object of the present invention to provide magnetic and electrical circuits of reduced weight and improved performance as compared to known transformers or the like apparatus of equal ratings.

It is also an object of the present invention to provide a novel method of assembling laminations from continuous steel strip rolled into a closed magnetic loop or core, and to provide facilities for application of the coils and the insulation of the electrical circuit withinthe symmetrical closed magnetic loops thus formed.-

Another important object of the present invention is to simplify the structure and shape of the laminations constituting the magnetic circuit, and to eliminate excess material, labor-and equipment required by present methods of core formation and application of coils and insulation.

Other important objects of my invention will be apparent from a reading of the following description taken in connection with the drawings, wherein for purposes of illustration I have shown preferred embodiments of myinvention.

In the drawings:

Figure 1 is a plan view of a transformer assembly produced in accordance with the present invention.

Figure 2 is a transverse vertical sectional view, enlarged, taken through Figure 1 approximately on the line 2-2 and looking toward the left in the direction of the arrows.

Figure 3 is an enlarged'transverse vertical sectional view taken through Figure 1 approximately on the line 33.

Figure 4 is a plan view of one of the steel strips used in forming the continuous loop cores, and showing a portion of uniform width, merging into portions of tapering width at weld points, the grain running. lengthwise in the said strip.

Figure 5 is an enlarged transverse vertical sectional view taken through Figure 6 approximately 0n the line 5-5.

Figure 6 is a side or endelevational view of one of the loop cores showing the manner in which the same is spirally wound and showing .its appearance after being pressed into the req r shape.

Figure '7 is an end or side elevational view of 5 I a press employed in pressing the loop cores after winding, to assume the oval or rectangular shape illustrated in Figure 6.

Figure 8 is a transverse vertical sectional view taken through Figure '7 approximately on the line 8-8 and looking toward the right in the direction of the arrows.

Figure 9 is a longitudinal sectional view taken through the combined core section mounting device and coil winder, and showing a core section in place therein.

Figure 10, is a transverse vertical sectional view taken through Figure 9 approximately on the line Ill-I 0 and looking toward the right in the direction of the arrows.

Figure 11 is a fragmentary detail transverse vertical sectional view taken through Figure 9 approximately on the line I ll l Figure 12 is an end elevational view looking from right to left in Figure 9. v

Referring in detail to the drawings, it will be apparent that in accordance with the present invention any desired core section may be produced, but for purposes of illustration, a polygonal-shaped core section, which gives the maximum cross section area for a given enclosing cir-' cle is shown. Strips of tapered width and strips of uniform width are employed selectively in proper combination to produce the desired core section. A strip of uniform width throughout 85 its length will form a rectangular or square core section, while a polygonal-shaped core section, such as that shown herein, requires the utilization of two tapered elements designated l and 3, respectively, and one element designated 2, which 10 is of uniform width, joined together in end to end relationship to form one continuous strip,

,with the grain of the metal running longitudinally. The resulting taper is not great, as will be understood from consideration of the final 45 shape of the core section to be achieved, but this taper is gradual as indicated in Figure l of the drawings.

In forming a magnetic core by the method of the present invention, the strips I, 2 and 3 of magnetic steel are joined together by welding and then wound into an annular form of the required dimensions, by first passing the cold strip through a solid dielectric, of low melting point, such as parafiine, while said dielectric .is in its ll liquid state so as to form a film on the cold strip,

a and so as to separate the resulting laminations and provide a lubricant to facilitate the process of formation, and then placing the coiled strip in a press such as shown in Figure 7 of the drawings, to press and form into a rectangular shape. It is then placed in an annealing frame, also represented by the device shown in Figure '7 of the drawings, to support it during the annealing,

After the formed cores have beenfinished and k I tested, they are assembled and held together by suitable devices (not shown) such as clamps or steel-wires, to maintain the symmetry of the leg or core on which the coils are to be applied. when the core section is clamped-in the com- ,bined core section mounting device and winding device illustrated in Figures 9 through 12,

the core section is ready for application of the coils and insulation 4, by means of the collapsible winding form I3 which comprises the segments 5 banded together with wire Ill lying in circumferential grooves H, the segments 5 being tongueand groove connected as shown in Fi ure 10. p

The segments 5 have rack teeth l formed at their opposite ends which form a circular rack it which is operatively engaged by the spur gears or pinions l which are fixedly mounted on the r tatable rods 6, the rotation of which produces rotation of the coil winding form 93.

The rotatable rods 6 are equally radially spaced from a stationary shaft which is supported by passing through the stationary support 8 and the adjustable support 8', alongside of the rods 6 which turn in the elements 8 and 8'. Mounted on the right hand end of the shaft 5' is the idler gear 6' which is meshed with the" pinions 9 which are fastened to the projectin ends of the shafts 6, whereby all of the shafts 6 are rotated at the same speed when a crank or other rotating mechanism is applied to any one of the shafts 6, for rotating the coil form 63 at the desired speed and in the desired direction. As shown in Figure 9 of the drawings, the support 8 is stationary with the base i5 and this base is provided with a pair of tracks is with which slidably engage the openings in the lower part of the adjustable support element 8', which part of the support 8' is equipped with a clamping bolt I! to be turned down against the top of the base to lock the support element 8' in the adjusted position on-the base, suitable to accommodate the length of the core sections and coil forms to be wound. Of course, the stops i8 on the shaft 5' and IS on the shafts 6 are provided ammo of the core sectionsto be mounted and wound, are the holding blocks 22 whichslide between pairs ofguides 23 and-are-held in position by adjustable bolts 24 which are threaded in lugs 25 on the sides of the support elements, the working faces of the blocks 22 being' shaped to conform generally with the portion of the core sections to be engaged. In the present instance, three of the arrangements just described are'provided to accommodate the three core sections employed in the illustrated example, and these are equally spaced angularly and will be adjusted to cause the blocks 22 to be at equal radial distances from the center of the shaft 5, so that the core sections engaged by the facing pairs of holders will be properlypositioned relatively to each other for the winding operation. The arrangement of the core sections around the shaft 5' and the manner in which these sections are clamped toward the center of the arrangement by the blocks 22 and-bolts 24 is more readily observable from Fig. 10. a

With the core section in place in the combined core section mounting and winding device as described, and with the coil form l3 rotated at the proper speed, and with "the proper wire fed around and along the form l 3, by paying the wire 1 from-a suitable reel or the like (not shown) the coil will be wound on the form l3, whereupon the wires .lli' are cutand withdrawn, so as to permit removalof the winding drum segments 5. When the segments have been removed, the insulated fillers 26 and 21' (Fig.3) are put intocambrictape applied to the coil 28 by winding v such tape around the bundle of wires forming the coil and proceeding progressively around the coil the successive turns of tape being suitably lapped. It will be necessary; of course, to perform the wrapping operation at an exposed portion of the coil 28 between core sections and to turn the coil in the corewindows gradually until tape has been wrapped along the entire periphcry of the coil 28. The insulated fillers 26 and 27 are obviously not put in place until the tape wrapping d has been applied, as the fillers 26 and 27 not only serve as additional insulation but also help to hold the coil 28 in a fixed position. Owing to the fact that the core strip material is tapered, the core section 3| of the core has the shape of a geometric figure, the'sides of which are slanting or inclined so that, as shown in Figure 1, the cores may be fitted closely together inorder to obtain a high spacefactor of the magnetic material, that is, so as to-make the cross sectional area of the core material a relatively high fraction of the cross sectional area of the opening or window in the conductive winding structure or coil 28. The necessary wedges 32 are then installed between the inner periphery of the coil 28 and the two adjacent core sections as illustrated in Figure '1 of the drawings. Figures 2 and 3 show particularly the arrangement of the fillers. Itis'to be noted that the segments 5 forming the winding form It have slots in the ends thereof and opening into the grooves II' to facilitate cutting of the wires l0 therein in the operation of collapsing the winding form. Suchslots consist of the spaces between the teeth I of the rack I2, for as shown in Fig. 11 these spaces extend through the segments 5 of the winding form l3.

In the present general transformer practice followed by all manufacturers, the magnetic circuit consists of I, L, or E-shaped laminations punched or sheared from large sheets of metal assembled in various forms with both single and multiple circuits, and from formed strips assembled concentrically with the ends overlapping, all functioning in the same general way, which is to form a closed loop or flux path around a coil placed on a part of the same which is called the core, while the other parts are designated as outer legs or as a yoke. In any case there is at least one, and in most cases there are two to four breaks in each individual lamination circuit, each adding to the total reluctance of the path.

By the use of continuous core loops or sections each wound from continuous strips, these joints are eliminated as well as other undesirable features, and it is made possible to use cylindrical coils which provide the shortest mean turn of copper and a more perfect winding with greater facility. Absence of theserjoints also eliminates magnetic hum or noise. Furthermore, the loops can be annealed and core loss tests made before applying the coils and insulation, thereby assuring uniform performance within close limits. The composite result of these provisions is a reduction in size, weight, and losses for a given core, coil and insulation combination, affording the designer a means of maintaining performace with an appreciable reduction in size and weight and a more symmetrical, uniform and rugged product.

Obviously, for a given core section and coil space, the weight of iron, copper, and insulation is reduced appreciably, and waste encountered in customary practice is entirely eliminated. Expensive dies or special equipment for stamping or cutting laminations are not required in the present invention, and it is, therefore, possible to use laminations of maximum thickness within the limits imposed by eddy current conditions and maximum content of elements such as silicon or nickel for improvement of magnetic properties. Furthermore, it is possible to gain satisfactory results with less material or better results with-the same material heretofore used for a given rating. The timesaved in core assembly more than compensates for any. extra time required for coil and insulation application. Also, the coils may be removed and rewound without dismantling the core in case of trouble requiring repairs.

The combined forming clamp and annealing frame shown in Figures 7 and 8 comprises essentially the top and bottom members 35 and 36 which are connected by the clamping rods 31 and 38 which are adjustable to produce the desired clamping action against the ends of the, core sec- 'tion, the core section in its annular form being designated by the numeral 3| in Figure '1,

elements 35 and 36 are the elements 39 and I which are traversed by clamping rods 4| and 42 which like the clamping rods 31 and 38 are arranged in pairs on opposite sides of the core section, with the pairs of rods 4| and 42 located outside of the pairs of clamping rods 31 and 38, as shown in Figure 7 of the drawings. The dotted lines designated 3| show the final shape of the core section as affected by the proper operation of the clamping rods.

Although I have shown and described herein preferred embodiments of the invention, as a transformer, and as apparatus for producing the same, and as a procedure for achieving such a transformer, it is to be definitely understood that I do not desire to limit the application of the invention thereto, but any change or changes may be made in the materials and in the structure and arrangement of parts, as well as in the sequence and duration of operation concerned, within the spirit of the invention and the scope of the subjoined claims.

The transformer and method of assembling.

what is sired rectangular core, blocking and pressing the wound strip into the desired rectangular shape,.

securing it in such shape and then annealing it.

2. A method of making an annular magnetic core for a transformer or the like, said method comprising the steps of passing a strip of magnetic sheet material through a liquefied substance normally solid of relatively low melting point greater than the normal ambient temperature, then winding the strip with its film of solid into annular form of the dimensions required to produce the finished core section, and raising the temperature of the strip above the ambient temperature to cause the film to liquefy and fiow out, leaving space between surfaces of the successive turns of strip.

3. A magnetic core for stationary induction apparatus comprising a plurality of .core elements arranged radially about an axis, with the sides nearest the axis fitted together to form a leg on which current conducting wire may be wound, each of said core elements being composed of substantially continuous magnetically permeable metal strip material wound upon itself to constitute a closed magnetic loop, said metallic strip being of varying width decreasing toward both ends of the stripto cause the cross section of the core element to be of a substantially octagonal shape with slanting sides, whereby relatively high space factor of the magnetic strip material may be obtained.

HOMER M. SANDERS. 

